Hello everyone,
a few months ago, we had an initial meeting with a construction manager/developer. Together, we discussed a KfW70 standard house (for funding reasons) with a gas boiler and solar thermal system. It was said to be no problem.
Yesterday, the statement came from the responsible architect, who is also officially listed as a KfW consultant (see KfW website), that her program/calculator shows our desired KfW70 house would only be achievable with a heat pump. If we still want a gas boiler with solar thermal, we would need to make some "adjustments" to the windows (something to do with noble gas filling).
I always thought a KfW70 house consumes only 70% of the energy of a reference house, which, in my understanding, is reflected in the insulation. Are the heating systems also compared in their specific energy consumption?
a few months ago, we had an initial meeting with a construction manager/developer. Together, we discussed a KfW70 standard house (for funding reasons) with a gas boiler and solar thermal system. It was said to be no problem.
Yesterday, the statement came from the responsible architect, who is also officially listed as a KfW consultant (see KfW website), that her program/calculator shows our desired KfW70 house would only be achievable with a heat pump. If we still want a gas boiler with solar thermal, we would need to make some "adjustments" to the windows (something to do with noble gas filling).
I always thought a KfW70 house consumes only 70% of the energy of a reference house, which, in my understanding, is reflected in the insulation. Are the heating systems also compared in their specific energy consumption?
Now, the house is an overall system, and the calculation includes everything, not just the insulation... but usually, for KfW 70, you either need very good double glazing or simple triple glazing.
However, it also depends on the rest of the wall structure, heating system, with or without controlled ventilation, and so on.
However, it also depends on the rest of the wall structure, heating system, with or without controlled ventilation, and so on.
The KfW standard reflects both the building envelope (walls, windows, and roof) and the primary energy consumption, meaning the type of heating system used. You can adjust various factors to meet the KfW 70 standard. Ultimately, your choice depends on your preferences (such as renewables with solar thermal or using a heat pump) and your budget. I would consider two options and ask for calculations to be made. When talking with developers, I would always prepare a brief summary of the results and send it to the developer by email to ensure that both parties have a clear and accurate understanding of what was discussed.
For KfW70 certification, the H'T value ("how well the house is insulated") of the reference house must be at least 15% lower, and the Qp ("how much primary energy the house consumes") must be reduced by 30%.
When it comes to the heat pump, the Qp target cannot be met using gas and solar alone. Here, for example, a controlled ventilation system or a small photovoltaic system—or other options—could help. It is not necessarily required to make changes to the building envelope, although that might be the most cost-effective solution.
Another question: Why do you want KfW70? The interest rates have become unattractive at 1.4% (1.4% is also available directly from Ing-Diba!).
Furthermore, KfW certification and construction supervision also cost money. My general contractor roughly credited me €3,000 if we skip the KfW70 certification (the house still meets the KfW70 standard, but it’s just a matter of paperwork).
When it comes to the heat pump, the Qp target cannot be met using gas and solar alone. Here, for example, a controlled ventilation system or a small photovoltaic system—or other options—could help. It is not necessarily required to make changes to the building envelope, although that might be the most cost-effective solution.
Another question: Why do you want KfW70? The interest rates have become unattractive at 1.4% (1.4% is also available directly from Ing-Diba!).
Furthermore, KfW certification and construction supervision also cost money. My general contractor roughly credited me €3,000 if we skip the KfW70 certification (the house still meets the KfW70 standard, but it’s just a matter of paperwork).
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